It is known that 2,5-diphenylterephthalic acid is useful as a monomer in the preparation of liquid-crystalline polyesters. U.S. Pat. No. 3,365,425, describes polyesters prepared from ethylene glycol, terephthalic acid, and an asymmetrically substituted phthalic acid selected from 2,5-diphenylterephthalic acid, 4,6-diphenylisophthalic acid, and 5-t-butylisophthalic acid. In this patent, the 2,5-diphenylterephthalic acid is prepared by treatment of p-xylene with cyclohexene in the presence of AlCl.sub.3 to provide 2,5-dicyclohexy-p-xylene, which is then dehydrogenated over 5% Pd/C and oxidized with KMnO.sub.4. (See also, F. Ebel and W. Deuschel, Chem. Ber., 89, 2794 (1956) and E. K. Weisburger and J. H. Weisburger, J. Org. Chem., 23, 1193 (1958.)